The question is.......Are you trying to build strength or are you trying to just get a work out and tone muscles, or are you trying to build muscle mass.
One way to build massive strength is to do pyramids. What you are doing is actually using one weight.
What I do is something like this:
12 reps of 220, 8 reps of 250 4 reps of 280 and couple reps of 300 and then back down.
In this scheme you will build strength and some muscle mass. You will not build as much muscle as other lifting methods. This is an old method but it does work and you will find that your strength will go incrementally up. You will get to point where you cant move up very quickly and then there are ways to move past these plateaus .
Now with this said. Bench pressing does not isolate muscles. It uses the pecs, part of the biceps, part of the triceps, the deltoids and part of the shoulder muscles.
Bench pressing is a show of strength and what I showed you above is one way to exercise for competitive lifting. I would personally try to isolate the muscles by doing flies or cross pulls for the pecs and doing some other exercise for the other muscles.
but to answer your question......If you are looking on building strength I wouldn't use just one weight in a set of reps. The idea of the pyramid is that you lift as much as you can. Therefore you test your muscles each time you lift. Now this can be dangerous if you haven't been lifting long so what you can do is use a lighter weights and work up to a maximum at 4 reps.
I hope this helped.